java - 操作图像的内存有效方法？

Question

我有一些代码可以获取两张图像并将它们的中间部分合并为一张图像。该代码可以工作，但使用大量内存，因此在某些内存不足的设备上会失败。

有什么方法可以提高这段代码的内存效率吗？

代码

private void convertImages(){
    ImageView imageView = (ImageView) findViewById(R.id.imageView);

    File leftFile = new File(Environment.getExternalStorageDirectory(), "images/left.jpg");
    File rightFile = new File(Environment.getExternalStorageDirectory(), "images/right.jpg");

    Bitmap left = BitmapFactory.decodeFile(leftFile.getAbsolutePath());
    Bitmap right = BitmapFactory.decodeFile(rightFile.getAbsolutePath());

    Rect srcRect = new Rect( (int)(left.getWidth()*0.25), 0, (int)(left.getWidth()*0.75), left.getHeight() );
    Rect dstRectLeft = new Rect( 0, 0, (int)(srcRect.width()/2), srcRect.height() );
    Rect dstRectRight = new Rect( (int)(srcRect.width()/2), 0, srcRect.width(), srcRect.height() );

    Bitmap outBitmap = Bitmap.createBitmap(srcRect.width(), srcRect.height(), Bitmap.Config.ARGB_8888);
    Canvas outCanvas = new Canvas(outBitmap);
    outCanvas.drawBitmap(left, srcRect, dstRectLeft, null);
    outCanvas.drawBitmap(right, srcRect, dstRectRight, null);

    imageView.setImageBitmap( outBitmap );
}

Answer 1

您可以尝试压缩。尝试这个有用的 imagecompressor 类，为了方便起见，将其复制并粘贴到此线程中:

Android: Compressing images creates black borders on left and top margin

压缩器 java 会将您的图片压缩到其大小的 1/10 左右，因此对于 3mb 的图片，它将变成 300kb。希望这能为您节省一些内存。

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.media.ExifInterface;

import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

import timber.log.Timber;

//http://voidcanvas.com/whatsapp-like-image-compression-in-android/
public class ImageCompressor {

    public ImageCompressor() {}

    public static String compressImage(String imagePath, Context context) {
        Bitmap scaledBitmap = null;
        String filename = "compressed_" +imagePath.substring(imagePath.lastIndexOf("/")+1);

        BitmapFactory.Options options = new BitmapFactory.Options();

//      by setting this field as true, the actual bitmap pixels are not loaded in the memory. Just the bounds are loaded. If
//      you try the use the bitmap here, you will get null.
        options.inJustDecodeBounds = true;
        Timber.e( "imagePath "+imagePath);
        Timber.e("filename "+filename);
        Bitmap bmp = BitmapFactory.decodeFile(imagePath, options);
        if (options == null) {
            Timber.e("zero bitmap");
        }
        int actualHeight = options.outHeight;
        int actualWidth = options.outWidth;
        float imgRatio = actualWidth / actualHeight;

        float maxHeight = actualHeight * 10/20;
        float maxWidth = actualWidth * 10/20;
        float maxRatio = maxWidth / maxHeight;

//      width and height values are set maintaining the aspect ratio of the image

        if (actualHeight > maxHeight || actualWidth > maxWidth) {
            if (imgRatio < maxRatio) {

                imgRatio = maxHeight / actualHeight;
                actualWidth = (int) (imgRatio * actualWidth);
                actualHeight = (int) maxHeight;

            } else if (imgRatio > maxRatio) {

                imgRatio = maxWidth / actualWidth;
                actualHeight = (int) (imgRatio * actualHeight);
                actualWidth = (int) maxWidth;

            } else {

                actualHeight = (int) maxHeight;
                actualWidth = (int) maxWidth;

            }
        }

//      setting inSampleSize value allows to load a scaled down version of the original image

        options.inSampleSize = calculateInSampleSize(options, actualWidth, actualHeight);

//      inJustDecodeBounds set to false to load the actual bitmap
        options.inJustDecodeBounds = false;

//      this options allow android to claim the bitmap memory if it runs low on memory
        options.inPurgeable = true;
        options.inInputShareable = true;
        options.inTempStorage = new byte[16 * 1024];

        try {
//          load the bitmap from its path
            bmp = BitmapFactory.decodeFile(imagePath, options);
        } catch (OutOfMemoryError exception) {
            exception.printStackTrace();

        }
        try {
            scaledBitmap = Bitmap.createBitmap(actualWidth, actualHeight, Bitmap.Config.ARGB_8888);
        } catch (OutOfMemoryError exception) {
            exception.printStackTrace();
        }

        float ratioX = actualWidth / (float) options.outWidth;
        float ratioY = actualHeight / (float) options.outHeight;
        float middleX = actualWidth / 2.0f;
        float middleY = actualHeight / 2.0f;

        Matrix scaleMatrix = new Matrix();
        scaleMatrix.setScale(ratioX, ratioY, middleX, middleY);

        Canvas canvas = new Canvas(scaledBitmap);
        canvas.setMatrix(scaleMatrix);
        canvas.drawBitmap(bmp, middleX - bmp.getWidth() / 2, middleY - bmp.getHeight() / 2, new Paint(Paint.FILTER_BITMAP_FLAG));

//      check the rotation of the image and display it properly
        ExifInterface exif;
        try {
            exif = new ExifInterface(imagePath);

            int orientation = exif.getAttributeInt(
                    ExifInterface.TAG_ORIENTATION, 0);
            Timber.e("Exif: " + orientation);
            Matrix matrix = new Matrix();
            if (orientation == 6) {
                matrix.postRotate(90);
                Timber.e( "Exif: " + orientation);
            } else if (orientation == 3) {
                matrix.postRotate(180);
                Timber.e( "Exif: " + orientation);
            } else if (orientation == 8) {
                matrix.postRotate(270);
                Timber.e( "Exif: " + orientation);
            }
            scaledBitmap = Bitmap.createBitmap(scaledBitmap, 0, 0,
                    scaledBitmap.getWidth(), scaledBitmap.getHeight(), matrix,
                    true);
        } catch (IOException e) {
            e.printStackTrace();
        } catch (NullPointerException e) {
            e.printStackTrace();
        }

        FileOutputStream out = null;

        try {

            out = context.openFileOutput(filename, Context.MODE_PRIVATE);
            scaledBitmap.compress(Bitmap.CompressFormat.JPEG, 90, out);

            out.close();

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
            return filename;
        }

    public static int calculateInSampleSize(BitmapFactory.Options options, int reqWidth, int reqHeight) {
        final int height = options.outHeight;
        final int width = options.outWidth;
        int inSampleSize = 1;
        if (height > reqHeight || width > reqWidth) {
            final int heightRatio = Math.round((float) height/ (float) reqHeight);
            final int widthRatio = Math.round((float) width / (float) reqWidth);
            inSampleSize = heightRatio < widthRatio ? heightRatio : widthRatio;      }
        final float totalPixels = width * height;
        final float totalReqPixelsCap = reqWidth * reqHeight * 2;
        while (totalPixels / (inSampleSize * inSampleSize) > totalReqPixelsCap) {
            inSampleSize++;
        }
        return inSampleSize;
    }

}
}